Two-dimensional character of internal rotation of furfural and other five-member heterocyclic aromatic aldehydes

•Internal rotation possesses a complex character for furfural and similar molecules.•Found the strong kinematic interaction of CHO rotation and out-of-plane deformation•Taking account of this interaction gives a very good agreement with experiments.

The features of nuclear motion corresponding to the rotation of the formyl group (CHO) are studied for the molecules of furfural and some other five-member heterocyclic aromatic aldehydes by the use of MP2/6-311G** quantum chemical approximation. It is demonstrated that the traditional one-dimensional models of internal rotation for the molecules studied have only limited applicability. The reason is the strong kinematic interaction of the rotation of the CHO group and out-of-plane CHO deformation that is realized for the molecules under consideration. The computational procedure based on the two-dimensional approximation is considered for low lying vibrational states as more adequate to the problem.

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